if you truncate the log w/o backing it up, it will be lost (inactive transctions). You can modify your maintenance plan to include log backups, or just simply set your recovery model to simple...which is probably the best option for you.

Message
Executed as user: IHS\SqlAdmin. The transaction log for database 'P58' is full. To find out why space in the log cannot be reused, see the log_reuse_wait_desc column in sys.databases [SQLSTATE 42000] (Error 9002)Unable to open Step output file. The step failed.

Ritesh,
acperkins is right...there is nothing to shrink because the file is still full with inactive transactions. If you could just shrink it, then you wouldn't need to perform a log truncation. Read the first article I posted, I cover it.